This invention relates to erasable intermediate diazo-type paper. More specifically, it is concerned with a non-crinkling non-curling diazo-type erasable paper which has excellent image development and easy erasability using any of the conventional erasing means without leaving an image ghost. The invention contemplates the formation of light sensitive paper by first coating a light transmitting substrate material with a non-aqueous solution of an elastomeric barrier layer material followed by coating the barrier layer with a non-aqueous solution of a diazo containing composition to form a light sensitive diazo-type erasable paper.
For engineers, architects, designers and draftsmen, diazo-type intermediates perform two essential duties, as second originals and as base elements for revision of old, or composition of new drawings. When revising drawings and composing new drawings, all repetitive elements of the drawings are diazo-typed and only new information is drawn. This constructive usage requires a superior base paper with a superior drawing surface. Marring the surface, such as made by correction fluids, is to be avoided. The erasable diazo-type intermediates have enabled drawings to be erased by simple erasing thus providing the drafting professions with a valuable tool. The diazo-type papers allow erasure by the interposition of one or more interlayers, or barrier layers, between the base paper, film or cloth and the diazo or sensitizing layer. Any suitable interlayer must of necessity combine good hold-out against penetration or migration of the diazo compounds while possessing a strong affinity for the barrier layer. Qualities sought in an erasable diazo intermediate paper are good pencil and ink receptivity, visual transparency, manual and mechanical erasability with little or no ghosting of the erased imprints, glossing or deterioration of the surface with good transparency to ultra-violet light permitting rapid diazo reproduction and no crinkling and curling.
It is known in the art to prepare erasable diazo-type paper, for example, by first coating transparentized paper with an aqueous solution of a polymeric material to form a barrier layer which is then overcoated with an aqueous solution of a diazo-type sensitizing solution. Material for accomplishing such intermediate paper is disclosed, for example, in U.S. Pat. No. 4,058,399, other prior art references disclosing the background, material and processes for preparing erasable paper are U.S. Pat. Nos. 2,423,768; 2,646,363; 2,861,008; 3,418,469; 3,624,021; 3,627,563 and 3,813,261. Unfortunately, erasable transparentized papers in general have a tendency to cause "ghosts", for example, when folded, erased or scratched. "Ghosts" are caused by fracture of the substances used to prepare the paper. Ghost lines resulting from fractures block light, causing undesirable lines to be formed in copies on other paper. Moreover, there has been the tendency of the known erasable diazo-type intermediate paper to more quickly yellow with any prolonged exposure to ultraviolet light. The known formulations for preparing diazo-type erasable paper also exhibit a tendency to cause crinkling, curling and/or wrinkling during one or more stages of manufacture and in the finished product resulting in numerous disadvantages in the use of such papers. It will be appreciated in the art that while the known diazo-type erasable papers have made a valuable contribution to the art, for the most part, the heretofore known erasable papers lack one or more of the qualities most desirable in an erasable intermediate type paper.